With the scaling down of patterns of semiconductor integrated circuits, there have recently been proposed so-called “buried wiring structures,” in which fine contact holes, trenches, etc. having a high aspect radio are buried with a wiring material such as Cu or Al.
However, these buried wiring structures are disadvantageous in that when the main wiring material is, e.g., Cu, it tends to diffuse into the insulating film, thereby causing problems. Therefore, a conductive barrier film is provided between the insulating film and the wiring material to limit or prevent diffusion of Cu. Various methods of forming this barrier film have been proposed. For example, one known method is to deposit a material layer of Ta, TiN, TaN, etc. using PVD, MOCVD, or ALD to form a barrier film (see, e.g., Patent Document 1).
ALD is a technique of forming a desired metal film by first causing a precursor of one type to be adsorbed on the substrate surface (adsorption process), then supplying another precursor to the adsorbed precursor so that they contact and react with each other on the substrate surface (modification process), and then repeating these processes. Generally, ALD has an advantage over CVD in that it can be performed at lower temperature and allows for formation of a film having better coverage.
Incidentally, in addition to Ta and TiN films, ZrB2 films are known to have good barrier properties. As is known in the art, a ZrB2 film can be formed from Zr(BH4)4 material according to the reaction formula (I) below.Zr(BH4)4→ZrB2+B2H6+5H2  (1)
The reaction (1) above is practically effected by thermally decomposing the raw material by the direct heat from the Si substrate, thereby forming a ZrB2 film on the substrate. However, in order to form a good ZrB2 film, this method requires that the substrate be heated to 550° C. or more, which is not desirable.
One way to avoid this problem is a known CVD technique which forms a ZrB2 film on the Si substrate by adding hydrogen radicals to the material and then causing the material to react at low temperature (namely, 300-350° C.) by the heat from the hydrogen radicals and the substrate (see, e.g., Nonpatent Document 1).
Such addition of hydrogen radicals requires excitation of hydrogen gas. One known apparatus for exciting such gas is a microwave-excited plasma processing apparatus that uses a waveguide for introducing a microwave (see, e.g., Patent Document 2).    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-6856 (Claim 3, FIG. 4, etc.)    Patent Document 2: Japanese Laid-Open Patent Publication No. 10-255998 (Claim 1, FIG. 1, etc.)    Nonpatent Document 1: J. Appl. Phys., Vol. 91, No. 6, 15 Mar. 2002, pp. 3904-3907 (p. 3904)